High-carb under challenge

20 August 2001

Published in The Age

Ten thousand years after the Agricultural Revolution began converting hunter-gatherers into farmers, the high-carbohydrate diet is under challenge.

Governments and doctors have long-prescribed carbohydrate as our major dietary component, and Western consumers have happily embraced the high-carbohydrate diet.

“Carbs” bridge even the chasm between mainstream dieticians and alternative practitioners. Hospitals may lean to pasta and spuds, and naturopaths to Essene bread and fresh fruit, but both “medical” and holistic schools see carbs as the primary source of calories (food-energy) for humans.

But protein is making a comeback.

In the last five years new ideas have emerged - not from one discovery, or one side of the holistic-mainstream fence, but from dozens of studies and several schools of nutrition along the spectrum.

Perhaps the ground floor of the new approach is the recent science of “Evolutionary Diet” - which has brought together biologists, anthropologists, archaeologists, botanists and others in a quest to learn what foods we humans are adapted to.

The doyen of this new science (also known as “Paleodiet”) is Loren Cordain, Professor of Health at the University of Colorado. Cordain and colleagues have surveyed 229 hunter-gatherer societies across the globe - societies which probably live similarly to the vast majority of human ancestors.

The Age asked Professor Cordain what was the ratio of plant to animal food in the societies he studied:

“In terms of calories consumed, the estimated mean worldwide plant to animal ratio we calculated was 35:65,” he said.

The present plant-animal ratio in the US diet is 62:38 - a near-reversal of the apparent evolutionary pattern. A calorie table of Cordain’s makes it clear what large implications this has for the protein-carbohydrate balance:

We may now eat over 50 percent more fat than we are adapted to by evolution - and much of it "new" fats, notably those in oils and dairy. But the larger difference is in our protein consumption. This, if modern hunter-gatherers are any guide, is less than than half what it was during the formative period of Homo sapiens.

Evolutionary Diet enthusiasts believe there’s evidence in the archaeological record to support their claims. But the US archaeologist William Rathje, Research Professor at Stanford University, says human bone-dating techniques are too uncertain for this.

“No-one really knows what the mix of meat and other foods was in the Paleolithic and Neolithic. I know there are studies today on the composition of bones that give indications of diet nutrients,” he adds. “But how many specimens have been tested? Everyone probably got different quantities of meat based on their status in the community - high status getting more. So just a few samples mean very little.”

Professor Rathje says that the Paleodiet movement “can make suggestions, but it shouldn't set agendas just yet”.

Nevertheless, protein is today riding a surge of popularity, thanks largely to two best-selling health authors: Dr Barry Sears - who fathered the “Zone” diet - and Dr Robert Atkins. Between them, they have shifted the spotlight from fat - former public enemy number one - to carbohydrate.

Dr Sears is a former drug scientist who applied his understanding of drug delivery to carbohydrate metabolism. When the carbohydrate quotient of our meals is too high, he says, excessive insulin is released. This makes us fat - and sluggish physically and mentally, by reducing blood sugar levels to the brain. It also sets us up for longer term health problems: elevated insulin, claims Dr Sears, is the primary predictor of heart attack.

Sears accepts that carbohydrate is an essential nutrient. His complaint is that Western society consumes too much of it in proporton to protein. He cautions against eating many “dense” (glucose-rich) carbs like bread and pasta, and directs his readers towards lighter ones such as fruits and vegetables.

Dr Robert Atkins’s 1992 book “The New Diet Revolution” sold 10 million copies. A New York medico specialising in cardiology, Atkins’s bottom line is also reducing carbohydrate and increasing protein.

While there are some serious differences between the Zone and Atkins diets, both have a strong focus on “low glycaemic index” foods. The glycaemic index measures how quickly glucose is absorbed after eating, how far blood-glucose rises, and how quickly it returns to normal. For both authors, “high glycaemic index” foods - like bread and mashed potatoes - increase cardiovascular risk.

Caryl Nowson of the Dieticians’ Association of Australia disagrees: “If we look at epidemiological studies, the protection against cancer and cardiovascular disease is in the high carbohydrate diet, with more fruits and vegetables high in antioxidants, and low in fat.”

As for the the palaeolithic diet, Nowson says, “We were designed to manage on a very wide range of dietary intakes - from less than 10% protein to up to 35-40% protein.”

Cordain’s research on modern hunter-gatherers supports this - though it also concludes that on average today’s hunter-gatherers (our paleolithic “surrogates”) eat protein near the upper end of Nowson’s scale.

Nowson is also concerned that “there are some potential concerns with respect to the increased load on the kidneys” with higher-protein diets.

A study of the Atkins diet on 41 patients, by the Durham Medical Center in North Carolina, found no kidney problems. (Though the four-month trial may have been too short for such problems to develop.) The patients also lost an average 21 pounds.

Team leader Dr Eric C Westman, Assistant Professor of Medicine at Duke University, said: “We were able to confirm scientifically what Dr Atkins states he has seen in his practice over the past decades. The diet lowers cholesterol and triglycerides and raises HDL [“good cholesterol”]...which may represent an entirely new approach to the control and prevention of heart disease.”

The recent research is focussing some heat on the World Health Organisation’s macronutrient intake recommendations, which have been adopted by the Australan Government. These counsel a diet of 15-30 percent fat, 10-15 percent protein and 55-75 percent carbohydrate: vastly different balances from those likely eaten by our ancestors, and recommended by the likes of Sears and Atkins.

The famed “US food pyramid” is also at odds with the new thinking, with its broad base containing bread, cereal, rice and pasta. The Australian Association of Dieticians recommends 30 percent energy from fat, 50-60 percent from carbs, and 12-15 percent from protein. It “does not recommend the Atkins or Zone diets for the long-term”.

Australia’s best-known nutritionist, Rosemary Stanton, is likewise no fan of the Zone and Atkins diets:

“In the US they have a National Weight Control Register. Over 99 percent of people who lost weight and kept it off have done it with a low-fat diet and exercise. Less than 1 precent have followed a low-carbohydrate diet.”

As for the Paleodiet, Stanton says: “It was probably a very good diet for reproduction. But it’s not a very good diet for longevity. They didn’t live very long. They reproduced and then died.”

Despite all the disagreement, the usefulness of the present debate may be in switching public attention from the million side-issues in health, and putting it - at last - on the three “macronutrients” which make up the vast majority of our food intake.